(PureBasic) Encrypt a file to a PKCS7 encrypted message using multiple certificates from different users

Demonstrates how to encrypt a file to a PKCS7 encrypted message using multiple certificates from different users. Any one of the users can decrypt using his/her own certificate + private key.

Note: When doing public key encryption, it is the public key that is used to encrypt. The private key is required for decryption.

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IncludeFile "CkBinData.pb"
IncludeFile "CkCert.pb"
IncludeFile "CkCrypt2.pb"

Procedure ChilkatExample()

    ;  This example requires the Chilkat Crypt API to have been previously unlocked.
    ;  See Unlock Chilkat Crypt for sample code.

    crypt.i = CkCrypt2::ckCreate()
    If crypt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ;  Tell the crypt object to use 3 certificates.
    ;  Do this by calling AddEncryptCert for each certificate.

    ;  Load a digital certificate.
    ;  We don't need the private key for encryption.
    ;  Only the public key is needed (which is included in a certificate).
    cert1.i = CkCert::ckCreate()
    If cert1.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkCert::ckLoadFromFile(cert1,"qa_data/user1/cert_user1.pem")
    ;  Assume success for the example, but make sure your application checks for success/failure...
    CkCrypt2::ckAddEncryptCert(crypt,cert1)

    cert2.i = CkCert::ckCreate()
    If cert2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkCert::ckLoadFromFile(cert2,"qa_data/user2/cert_user2.pem")
    CkCrypt2::ckAddEncryptCert(crypt,cert2)

    cert3.i = CkCert::ckCreate()
    If cert3.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkCert::ckLoadFromFile(cert3,"qa_data/user3/cert_user3.pem")
    CkCrypt2::ckAddEncryptCert(crypt,cert3)

    ;  Indicate that we want PKI encryption (i.e. public-key infrastructure)
    ;  to produce a CMS message (Cryptographic Message Syntax/PKCS7),
    ;  that is be created with RSAES-OAEP padding, SHA256, and AES-128 for the
    ;  bulk encryption.
    CkCrypt2::setCkCryptAlgorithm(crypt, "pki")
    CkCrypt2::setCkPkcs7CryptAlg(crypt, "aes")
    CkCrypt2::setCkKeyLength(crypt, 128)
    CkCrypt2::setCkOaepHash(crypt, "sha256")
    CkCrypt2::setCkOaepPadding(crypt, 1)

    ;  Load the file to be encrypted...
    fileData.i = CkBinData::ckCreate()
    If fileData.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkBinData::ckLoadFile(fileData,"qa_data/jpg/penguins.jpg")
    ;  Your app should check for success/failure..

    ;  Encrypt the data.  The contents of the fileData object are replaced with the PKCS7 encrypted message.
    success = CkCrypt2::ckEncryptBd(crypt,fileData)
    If success <> 1
        Debug CkCrypt2::ckLastErrorText(crypt)
        CkCrypt2::ckDispose(crypt)
        CkCert::ckDispose(cert1)
        CkCert::ckDispose(cert2)
        CkCert::ckDispose(cert3)
        CkBinData::ckDispose(fileData)
        ProcedureReturn
    EndIf

    ;  Save the PKCS7 encrypted message to a file..
    success = CkBinData::ckWriteFile(fileData,"qa_output/pkcs7_encrypted.p7")

    ;  Now indicate that the PKCS7 output is to be returned in the base64 encoding.
    CkCrypt2::setCkEncodingMode(crypt, "base64")

    Debug "OK."


    CkCrypt2::ckDispose(crypt)
    CkCert::ckDispose(cert1)
    CkCert::ckDispose(cert2)
    CkCert::ckDispose(cert3)
    CkBinData::ckDispose(fileData)


    ProcedureReturn
EndProcedure